DESCRIPTION: The objectives of this work are to elucidate the mechanisms regulating the level of expression of the mdm2 oncogene and to define the mechanisms by which MDM2 proteins stimulate proliferation. Mdm2 is overexpressed in several types of human tumors and is likely to contribute to the development of cancer because MDM2 proteins antagonize the functions of two tumor suppressor proteins, p53 and the retinoblastoma protein. Overexpression of mdm2 can reverse the block in progression through the cell cycle mediated by either Rb or p53, indicating that constitutively high levels of MDM2 may allow cells to escape the controls that protect against tumor formation. Expression of mdm2 is induced in cells exposed to ultra-violet (UV) light. The induction of MDM2 expression requires functional p53, which is a transcriptional activator. Induction of mdm2 expression results in synthesis of two mRNAs and two major species of MDM2 protein. The larger MDM2 protein binds to and inhibits p53, forming a regulatory loop. The function of the smaller protein is unknown. It is proposed to investigate the regulation of mdm2 expression during the UV-response by determining the rate of transcription of both mRNAs and by mapping mdm2 gene sequences required for this induction. Dr. Perry will identify the translational start site of the smaller MDM2 protein using mutational analysis and peptide mapping. Then, the functional domains of MDM2 required for two of its effects on cellular proliferation: cooperation with the Ha-ras oncogene in transformation and stimulation of expression of genes containing E2F sites, will be determined. Finally, Dr. Perry will use two new approaches to study MDM2's growth-stimulatory effects and to identify novel cellular phenotypes resulting from mdm2 overexpression.